Process for the synthesis of 2,5-dihydroxyterephthalic acid

ABSTRACT

2,5-dihydroxyterephthalic acid is produced in high yields and high purity from 2,5-dihaloterephthalic acid by contact with a copper source and a ligand that coordinates to copper under basic conditions.

TECHNICAL FIELD

This invention relates to the manufacture of hydroxybenzoic acids, whichare valuable for a variety of purposes such as use as intermediates oras monomers to make polymers.

BACKGROUND

Hydroxybenzoic acids are useful as intermediates in the manufacture ofmany valuable materials including pharmaceuticals and compounds activein crop protection, and are also useful as monomers in the production ofpolymers. In particular, 2,5-dihydroxyterephthalic acid (Formula I,“DHTA”) is a useful monomer for the synthesis of high strength fiberssuch as those made frompoly[(1,4-dihydrodiimidazo[4,5-b:4′,5′-e]pyridine-2,6-diyl)(2,5-dihydroxy-1,4-phenylene)].

Various preparations of 2,5-dihydroxyterephthalic acid and otherhydroxybenzoic acids are known. Marzin, in Journal fuer PraktischeChemie, 1933, 138, 103-106, teaches the synthesis of2,5-dihydroxyterephthalic acid from 2,5-dibromoterephthalic acid(Formula II, “DBTA”) in the presence of copper powder.

Singh et al, in Jour. Indian Chem. Soc., Vol. 34, No. 4, pages 321˜323(1957), report the preparation of a product that includes DHTA by thecondensation of DBTA with phenol in the presence of KOH and copperpowder.

Rusonik et al, Dalton Transactions, 2003, 2024-2028, describe thetransformation of 2-bromobenzoic acid into salicylic acid, benzoic acid,and diphenoic acid in a reaction catalyzed by Cu(I) in the presence ofvarious ligands. A tertiary tetraamine minimizes the formation ofdiphenoic acid in use with Cu(I).

Comdom et al, Synthetic Communications, 32(13), 2055-59 (2002), describea process for the synthesis of salicylic acids from 2-chlorobenzoicacids. Stoichiometric amounts of pyridine (0.5 to 2.0 moles per mole of2-chlorobenzoic acid) are used such as at least 1.0 mole pyridine permole 2-chlorobenzoic acid. Cu powder is used as a catalyst along withthe pyridine.

The various prior art processes for making hydroxybenzoic acids arecharacterized by long reaction times, limited conversion resulting insignificant productivity loss, or the need to run under pressure and/orat higher temperatures (typically 140 to 250° C.) to get reasonablerates and productivity. A need therefore remains for a process by which2,5-dihydroxy terephthalic acid can be produced economically; with lowinherent operational difficulty; and with high yields and highproductivity in both small- and large-scale operation, and in batch andcontinuous operation.

SUMMARY

One embodiment of this invention provides a process for preparing2,5-dihydroxyterephthalic acid by (a) contacting a2,5-dihaloterephthalic acid (III)

where X=Cl, Br, or I

with base in water to form therefrom the corresponding dibasic salt of2,5-dihaloterephthalic acid; (b) contacting the dibasic salt of2,5-dihaloterephthalic acid with base in water, and with a copper sourcein the presence of a ligand that coordinates to copper, to form thedibasic salt of 2,5-dihydroxyterephthalic acid from the dibasic salt of2,5-dihaloterephthalic acid at a solution pH of at least about 8; (c)optionally, separating the dibasic salt of 2,5-dihydroxyterephthalicacid from the reaction mixture in which it is formed; and (d) contactingthe dibasic salt of 2,5-dihydroxyterephthalic acid with acid to formtherefrom 2,5-dihydroxyterephthalic acid.

Yet another embodiment of this invention provides a process forpreparing a 2,5-dialkoxyterephthalic acid by preparing a2,5-dihydroxyterephthalic acid in the manner described above and thenconverting the 2,5-dihydroxyterephthalic acid to a2,5-dialkoxyterephthalic acid.

Yet another embodiment of this invention consequently provides a processfor preparing 2,5-dialkoxyterephthalic acid by (a) contacting a2,5-dihaloterephthalic acid (III)

where X=Cl, Br, or I

with base in water to form therefrom the corresponding dibasic salt of2,5-dihaloterephthalic acid; (b) contacting the dibasic salt of2,5-dihaloterephthalic acid with base in water, and with a copper sourcein the presence of a ligand that coordinates to copper, to form thedibasic salt of 2,5-dihydroxyterephthalic acid from the dibasic salt of2,5-dihaloterephthalic acid at a solution pH of at least about 8; (c)optionally, separating the dibasic salt of 2,5-dihydroxyterephthalicacid from the reaction mixture in which it is formed; (d) contacting thedibasic salt of 2,5-dihydroxyterephthalic acid with acid to formtherefrom a 2,5-dihydroxyterephthalic acid; and (e) converting the2,5-dihydroxyterephthalic acid to a 2,5-dialkoxyterephthalic acid.

Yet another embodiment of this invention provides a process forpreparing a 2,5-dihydroxyterephthalic acid or a 2,5-dialkoxyterephthalicacid as described above that further includes a step of subjecting the2,5-dihydroxyterephthalic acid or the 2,5-dialkoxyterephthalic acid to areaction to prepare therefrom a compound, monomer, oligomer or polymer.

Yet another embodiment of this invention consequently provides a processfor preparing a compound, monomer, oligomer or polymer by (a) contactinga 2,5-dihaloterephthalic acid (III)

where X=Cl, Br, or I

with base in water to form therefrom the corresponding dibasic salt of2,5-dihaloterephthalic acid; (b) contacting the dibasic salt of2,5-dihaloterephthalic acid with base in water, and with a copper sourcein the presence of a ligand that coordinates to copper, to form thedibasic salt of 2,5-dihydroxyterephthalic acid from the dibasic salt of2,5-dihaloterephthalic acid at a solution pH of at least about 8; (c)optionally, separating the dibasic salt of 2,5-dihydroxyterephthalicacid from the reaction mixture in which it is formed; (d) contacting thedibasic salt of 2,5-dihydroxyterephthalic acid with acid to formtherefrom 2,5-dihydroxyterephthalic acid; (e) optionally, converting the2,5-dihydroxyterephthalic acid to a 2,5-dialkoxyterephthalic acid; and(f) subjecting the 2,5-dihydroxyterephthalic acid and/or the2,5-dialkoxyterephthalic acid to a reaction to prepare therefrom acompound, monomer, oligomer or polymer.

In yet another embodiment, the ligand in one or more of the processesdescribed herein may be a Schiff base.

DETAILED DESCRIPTION

This invention provides a high yield and high productivity process forpreparing a 2,5-dihydroxyterephthalic acid by contacting a2,5-dihaloterephthalic acid with base to form the dibasic salt of2,5-dihaloterephthalic acid; contacting the dibasic salt of2,5-dihaloterephthalic acid with base, and with a copper source in thepresence of a ligand that coordinates to copper, to form the dibasicsalt of 2,5-dihydroxyterephthalic acid; and then contacting the dibasicsalt of 2,5-dihydroxyterephthalic acid with acid to form the2,5-dihydroxyterephthalic acid product. The term “dibasic salt” as usedherein denotes the salt of a dibasic acid, which is an acid thatcontains two replaceable hydrogen atoms per molecule.

Suitable dihaloterephthalic acids with which the process of thisinvention is started include 2,5-dibromoterephthalic acid,2,5-dichloroterephthalic acid, and 2,5-diiodoterephthalic acid, ormixtures thereof. 2,5-dibromoterephthalic acid (“DBTA”)is commerciallyavailable. It can, however, be synthesized, for example, by oxidation ofp-xylene in aqueous hydrogen bromide (McIntyre et al, Journal of theChemical Society, Abstracts, 1961, 4082-5), by bromination ofterephthalic acid or terephthaloyl chloride (U.S. Pat. No. 3,894,079),or by oxidation of 2,5-dibromo-1,4-dimethylbenzene (DE 1,812,703).2,5-dichloroterephthalic acid is also commercially available. It can,however, be synthesized, for example, by oxidation of2,5-dichloro-1,4-dimethylbenzene [Shcherbina et al, Zhurnal PrikladnoiKhimii (Sankt-Peterburg, Russian Federation, 1990)], 63(2), 467-70.2,5-diiodoterephthalic acid can be synthesized, for example, byoxidation of 2,5-diiodo-1,4-dimethylbenzene [Perry et al, Macromolecules(1995), 28(10), 3509-15].

In step (a), 2,5-dihaloterephthalic acid is contacted with base in waterto form therefrom the corresponding dibasic salt of2,5-dihaloterephthalic acid. In step (b), the dibasic salt of2,5-dihaloterephthalic acid is contacted with base in water, and with acopper source in the presence of a ligand that coordinates to copper, toform the dibasic salt of 2,5-dihydroxyterephthalic acid from the dibasicsalt of 2,5-dihaloterephthalic acid.

The base used in step (a) and/or step (b) may be an ionic base, and mayin particular be one or more of a hydroxide, carbonate, bicarbonate,phosphate or hydrogen phosphate of one or more of Li, Na, K, Mg or Ca.The base used may be water-soluble, partially water-soluble, or thesolubility of the base may increase as the reaction progresses and/or asthe base is consumed. NaOH and Na₂CO₃ are preferred, but other suitableorganic bases may be selected, for example, from the group consisting oftrialkylamines (such as tributylamine);N,N,N′,N′-tetramethylethylenediamine; and N-alkyl imidazoles (forexample, N-methylimidazole). In principle any base capable ofmaintaining a pH above 8 and/or binding the acid produced during thereaction of the 2,5-dihaloterephthalic acid is suitable.

The specific amounts of base to be used in steps (a) and/or (b) dependon the strength of the base. In step (a), 2,5-dihaloterephthalic acid ispreferably contacted with at least about two equivalents of base,preferably a water-soluble base, per equivalent of2,5-dihaloterephthalic acid. One “equivalent” as used for a base in thiscontext is the number of moles of base that will react with one mole ofhydrogen ions; for an acid, one equivalent is the number of moles ofacid that will supply one mole of hydrogen ions.

In step (b), enough base should be used to maintain a solution pH of atleast about 8, or at least about 9, or at least about 10, and preferablybetween about 9 and about 11. Thus, typically in step (b), the dibasicsalt of 2,5-dihaloterephthalic acid is contacted with at least about twoequivalents of base, such as a water-soluble base, per equivalent of thedibasic salt of 2,5-dihaloterephthalic acid.

In alternative embodiments, however, it may be desirable in steps (a)and (b) to use a total of at least about 4 to about 5 equivalents ofbase, such as a water-soluble base, in the reaction mixture perequivalent of 2,5-dihaloterephthalic acid originally used at the startof the reaction. A base used in an amount as described above istypically a strong base, and is typically added at ambient temperature.The base used in step (b) may be the same as, or different than, thebase used in step (a).

As mentioned above, in step (b), the dibasic salt of2,5-dihaloterephthalic acid is also contacted with a copper source inthe presence of a ligand that coordinates to copper. The copper sourceand the ligand may be added sequentially to the reaction mixture, or maybe combined separately (for example, in a solution of water oracetonitrile) and added together. The copper source may be combined withthe ligand in the presence of oxygen in water, or be combined with asolvent mixture containing water.

From the presence together in the reaction mixture of the copper sourceand the ligand, in a basic solution of the dibasic salt of the2,5-dihaloterephthalic acid, there is obtained an aqueous mixturecontaining the dibasic salt of 2,5-dihydroxyterephthalic acid, copperspecie(s), the ligand, and a halide salt. If desired, the dibasic saltof 2,5-dihydroxyterephthalic acid may, at this stage and before theacidification in step (d), be separated from the mixture [as optionalstep (c)], and may be used as a dibasic salt in another reaction or forother purposes.

The dibasic salt of 2,5-dihydroxyterephthalic acid is then contacted instep (d) with acid to convert it to the 2,5-dihydroxyterephthalic acidproduct. Any acid of sufficient strength to protonate the dibasic saltis suitable. Examples include without limitation hydrochloric acid,sulfuric acid and phosphoric acid.

The reaction temperature for steps (a) and (b) is preferably betweenabout 60 and about 120° C., more preferably between about 75 and about95° C.; and the process thus in various embodiments involves a step ofheating the reaction mixture. The solution is typically allowed to coolbefore the acidification in step (d) is carried out. In variousembodiments, oxygen may be excluded during the reaction.

The copper source is copper metal [“Cu(0)”], one or more coppercompounds, or a mixture of copper metal and one or more coppercompounds. The copper compound may be a Cu(I) salt, a Cu(II) salt, ormixtures thereof. Examples include without limitation CuCl, CuBr, CuI,Cu₂SO₄, CuNO₃, CuCl₂, CuBr₂, CuI₂, CuSO₄, and Cu(NO₃)₂. CuBr ispreferred. The amount of copper provided is typically about 0.1 to about5 mol % based on moles of 2,5-dihaloterephthalic acid.

When the copper source is Cu(0), Cu(0), copper bromide and a ligand maybe combined in the presence of air. In the case of Cu(0) or Cu(I), apredetermined amount of metal and ligand may be combined in water, andthe resulting mixture may be reacted with air or dilute oxygen until acolored solution is formed. The resulting metal/ligand solution is addedto the reaction mixture containing the dibasic salt of2,5-dihaloterephthalic acid and base in water.

The ligand may be a Schiff base. The term “Schiff base” as used hereindenotes a functional group or type of chemical compound containing acarbon-nitrogen double bond with the nitrogen atom connected to an arylgroup or an alkyl group but not to hydrogen, such as shown in FormulaIV. It is typically the condensation product of a primary amine and aketone or aldehyde, produced by a reaction scheme such as the following:

wherein R¹, R² and R³ are each independently selected from substitutedand unsubstituted C₁-C₁₆ n-alkyl, iso-alkyl and tertiary alkyl groups;and substituted and unsubstituted C₆-C₃₀ aryl and heteroaryl groups.

In one embodiment, a Schiff base suitable for use herein as the ligandincludes a diimine such as described generally by Formula V

herein A is selected from the group consisting of

R¹, R², R³ and R⁴ are each independently selected from substituted andunsubstituted C₁-C₁₆ n-alkyl, iso-alkyl and tertiary alkyl groups; andsubstituted and unsubstituted C₆- C₃₀ aryl and heteroaryl groups;

R⁵ is selected from H, substituted and unsubstituted C₁-C₁₆ n-alkyl,iso-alkyl and tertiary alkyl groups; and substituted and unsubstitutedC₆-C₃₀ aryl and heteroaryl groups; and halogen;

R⁶, R⁷, R⁸ and R⁹ are each independently selected from H or asubstituted or unsubstituted C₁-C₁₆ n-alkyl, iso-alkyl or tertiary alkylgroup; and

n=0 or 1.

The term “unsubstituted”, as used with reference to an alkyl or arylgroup in a Schiff base as described above, means that the alkyl or arylgroup contains no atoms other than carbon and hydrogen. In a substitutedalkyl or aryl group, however, one or more O or S atoms may optionally besubstituted for any one or more of the in-chain or in-ring carbon atoms,provided that the resulting structure contains no —0—0— or —S—S—moieties, and provided that no carbon atom is bonded to more than oneheteroatom.

In another embodiment, a suitable diimine for use herein as the ligandincludes N,N′-dimesityl-2,3-diiminobutane (such as described generallyby Formula VI)

In this instance, n=0, R¹=R²=mesityl, and R³ and R⁴ are taken togetherto form the CH₃—C—C—CH₃ moiety bonded to the two nitrogen atoms.

In a further embodiment, a diimine suitable for use herein as the ligandincludes N,N′-di(trifluoromethylbenzene)-2,3-diiminoethane (such asdescribed generally by Formula VII)

In this instance, n=0, R¹=R²=(trifluoromethyl)benzyl, and R³ and R⁴ aretaken together to form the CH₃—C—C—CH₃ moiety bonded to the two nitrogenatoms.

A ligand suitable for use herein may be selected as any one or more orall of the members of the whole population of ligands described by nameor structure above. A suitable ligand may, however, also be selected asany one or more or all of the members of a subgroup of the wholepopulation, where the subgroup may be any size (1, 2, 6, 10 or 20, forexample), and where the subgroup is formed by omitting any one or moreof the members of the whole population as described above. As a result,the ligand may in such instance not only be selected as one or more orall of the members of any subgroup of any size that may be formed fromthe whole population of ligands as described above, but the ligand mayalso be selected in the absence of the members that have been omittedfrom the whole population to form the subgroup.

In various embodiments, the ligand may be provided in an amount of about1 to about 10, preferably about 1 to about 2, molar equivalents ofligand per mole of copper. As used herein, the term “molar equivalent”indicates the number of moles of ligand that will interact with one moleof copper.

When the 2,5-dihaloterephthalic acid is 2,5-dibromoterephthalic acid,the copper source may be Cu(0) and/or a Cu(I) salt, and it may becombined with the ligand in the presence of oxygen in water, or asolvent mixture containing water. Alternatively, when the Cu(I) salt isCuBr, and the ligand is one of the Schiff bases described specificallyabove [such as N,N′-dimesityl-2,3-diiminobutane orN,N′-di(trifluoromethylbenzene)-2,3-diiminoethane], the ligand may beprovided in an amount of two molar equivalents per mole of copper, andthe CuBr may be combined with the ligand in the presence of water andair.

The ligand is believed to facilitate the action of the copper source asa catalyst, and/or the copper source and the ligand are believed tofunction together to act as a catalyst, to improve one or moreattributes of the reaction.

The process described above also allows for effective and efficientsynthesis of related compounds, such as a 2,5-dialkoxy terephthalicacid, which may be described generally by the structure of Formula VI:

wherein R⁹ and R¹⁰ are each independently a substituted or unsubstitutedC₁-₁₀ alkyl group. R⁹ and R₁₀ are, when unsubstituted, univalent groupscontaining only carbon and hydrogen. In any of those alkyl groups,however, one or more O or S atoms may optionally be substituted for anyone or more of the in-chain carbon atoms, provided that the resultingstructure contains no —O—0— or —S—S— moieties, and provided that nocarbon atom is bonded to more than one heteroatom.

A 2,5-dihydroxy terephthalic acid, as prepared by the process of thisinvention, may be converted to a 2,5-dialkoxy terephthalic acid, andsuch conversion may be accomplished, for example, by contacting a2,5-dihydroxy terephthalic acid under basic conditions with a dialkylsulfate of the formula R⁹ R¹⁰ SO₄. One suitable method of running such aconversion reaction is as described in Austrian Patent No. 265,244.Suitable basic conditions for such conversion are a solution pH of atleast about 8, or at least about 9, or at least about 10, and preferablyabout 9 to about 11, using one or more bases such as described above.

In certain embodiments, it may be desired to separate the2,5-dihydroxyterephthalic acid from the reaction mixture in which it wasformed before converting it to a 2,5-dialkoxyterephthalic acid.

The process described above also allows for effective and efficientsynthesis of products made from the resulting 2,5-dihydroxyterephthalicacid or 2,5-dialkoxyterephthalic acid such as a compound, a monomer, oran oligomer or polymer thereof. These produced materials may have one ormore of ester functionality, ether functionality, amide functionality,imide functionality, imidazole functionality, carbonate functionality,acrylate functionality, epoxide functionality, urethane functionality,acetal functionality, and anhydride functionality.

Representative reactions involving a material made by the process ofthis invention, or a derivative of such material, include, for example,making a polyester from a 2,5-dihydroxyterephthalic acid and eitherdiethylene glycol or triethylene glycol in the presence of 0.1% ofZN₃(BO₃)₂ in 1-methylnaphthalene under nitrogen, as disclosed in U.S.Pat. No. 3,047,536 (which is incorporated in its entirety as a parthereof for all purposes). Similarly, a 2,5-dihydroxyterephthalic acid isdisclosed as suitable for copolymeriztion with a dibasic acid and aglycol to prepare a heat-stabilized polyester in U.S. Pat. No. 3,227,680(which is incorporated in its entirety as a part hereof for allpurposes), wherein representative conditions involve forming aprepolymer in the presence of titanium tetraisopropoxide in butanol at200˜250° C., followed by solid-phase polymerization at 280° C. at apressure of 0.08 mm Hg.

A 2,5-dihydroxyterephthalic acid has also been polymerized with thetrihydrochloride-monohydrate of tetraaminopyridine in strongpolyphosphoric acid under slow heating above 100° C. up to about 180° C.under reduced pressure, followed by precipitation in water, as disclosedin U.S. Pat. No. 5,674,969 (which is incorporated in its entirety as apart hereof for all purposes); or by mixing the monomers at atemperature from about 50° C. to about 110° C., and then 145° C. to forman oligomer, and then reacting the oligomer at a temperature of about160° C. to about 250° C. as disclosed in U.S. Provisional ApplicationNo. 60/665,737, filed Mar. 28, 2005 (which is incorporated in itsentirety as a part hereof for all purposes), published as WO2006/104974. The polymer that may be so produced may be apyridobisimidazole-2,6-diyl(2,5-dihydroxy-p-phenylene) polymer such as apoly(1,4-(2,5-dihydroxy) phenylene-2,6-pyrido[2,3-d:5,6-d′]bisimidazole) polymer, or apoly[(1,4-dihydrodiimidazo[4,5-b:4′,5′-e]pyridine-2,6-diyl)(2,5-dihydroxy-1,4-phenylene)] polymer. The pyridobisimidazole portionthereof may, however, be replaced by any or more of a benzobisimidazole,benzobisthiazole, benzobisoxazole, pyridobisthiazole and apyridobisoxazole; and the 2,5-dihydroxy-p-phenylene portion thereof maybe replace the derivative of one or more of isophthalic acid,terephthalic acid, 2,5-pyridine dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-diphenyl dicarboxylic acid, 2,6-quinolinedicarboxylic acid, and 2,6-bis(4-carboxyphenyl)pyridobisimidazole.

EXAMPLES

This invention is further defined in the following examples. Theseexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, and do not limit the scope of theappended claims. From the above discussion and these examples, theessential characteristics of this invention may be ascertained, and,without departing from the spirit and scope thereof, modifications ofthe invention may be made to adapt it to various uses and conditions.

Materials: The following materials were used in the examples. Allreagents were used as received. Product purity was determined by ¹H NMR.

The N,N′-dimesityl-2,3-diiminobutane was made following the procedure inJournal of the American Chemical Society (2002), 124 (7) 1378-1399. The2-aminobenzotrifluoride (also known as “2-(trifluoromethyl)aniline” )(99% purity, catalog number A4,160-7) and 2,3-butandione (97% purity,catalog number B8,530-7) were obtained from the Aldrich Chemical Company(Milwaukee, Wis., USA).

The 2,5-dibromoterephthalic acid (95+% purity) was obtained fromMaybridge Chemical Company Ltd.(Cornwall, United Kingdom). Copper(I)bromide (“CuBr”) (98% purity) was obtained from Acros Organics (Geel,Belgium). Na₂CO₃ (99.5% purity) was obtained from EM Science (Gibbstown,N.J.).

As used herein, the term “conversion” denotes to how much reactant wasused up as a fraction or percentage of the theoretical amount. As usedherein, the term “selectivity” for a product P denotes the molarfraction or molar percentage of P in the final product mix. Theconversion times the selectivity thus equals the maximum “yield” of P;the actual or “net” yield will normally be somewhat less than thisbecause of sample losses incurred in the course of activities such asisolating, handling, drying, and the like. As used herein, the term“purity” denotes what percentage of the in-hand, isolated sample isactually the specified substance.

The terms “H₂O” and “water” refer to distilled water. The meaning ofabbreviations is as follows: “h” means hour(s), “min” means minute(s),“mL” means milliliter(s), “g” means gram(s), “mg” means milligram(s),“mol” means mole(s), “mol equiv” means molar equivalent(s), “mmol” meansmillimole(s), “D” means density, “IR” means infrared spectroscopy, and“NMR” means nuclear magnetic resonance spectroscopy.

EXAMPLE 1

This example demonstrates the formation of 2,5-dihydroxyterephthalicacid from 2,5-dibromoterephthalic acid using CuBr andN,N′-dimesityl-2,3-diiminobutane

N,N′-dimesityl-2,3-diiminobutane

Under nitrogen, 2.00 g (6.2 mmol) of 2,5-dibromoterephthalic acid werecombined with 10 g of H₂O; 0.679 g (6.4 mmol) of Na₂CO₃ was then added.The mixture was heated to reflux with stirring for 30 min, remainingunder a nitrogen atmosphere. Another 0.950 g (9.0 mmol) of Na₂CO₃ wasadded to the reaction mixture and reflux was continued for 30 min.Separately, 9 mg (0.01 mol equiv) of CuBr and 40 mg (0.02 mol equiv) ofN,N′-dimesityl-2,3-diiminobutane were combined with 2 mL H₂O undernitrogen. The resulting mixture was stirred under an air atmosphereuntil the CuBr was dissolved. This solution was added to the stirredreaction mixture via syringe at 80° C. under nitrogen and stirred for 30h at 80° C. After cooling to 25° C., the reaction mixture was acidifiedwith HCl (conc.), producing a dark yellow precipitate. The yellowprecipitate was filtered and washed with water. After drying, a total of1.09 g of crude 2,5-dihydroxyterephthalic acid was collected. The purityof 2,5-dihydroxyterephthalic acid was determined by ¹H NMR to be about81%. The net yield of 2,5-dihydroxyterephthalic acid was determined tobe 72%.

EXAMPLE 2

N,N′-di(trifluoromethylbenzene)-2,3-diiminoethane was prepared asfollows: a mixture of 10.2 mL (13.1 g; 81.2 mmol; D=1.28)2-aminobenzotrifluoride and 3.6 mL (3.5 g; 41 mmol; D=0.98)freshly-distilled 2,3-butandione in 15 mL methanol containing 6 drops of98% formic acid was stirred at 35° C. under nitrogen for 8 days. Arotovap was used to remove solvent from the reaction mixture, and theresultant crystalline solids (1.3 g) were washed with carbontetrachloride. The crystals were dissolved in chloroform; the solutionwas passed through a short alumina column and evaporated to yield 1.0 gof yellow crystals of the diimine. ¹H NMR (CDCl₃): 2.12 ppm (s, 6 H,CH3); 6.77 (d, 2 H, ArH, J=9 Hz); 7.20 (t, 2 H, ArH, J=7 Hz); 7.53 (t, 2H, ArH, J=7 Hz); 7.68 (t, 2 H, ArH, J=8 Hz). IR: 1706, 1651, 1603, 1579,1319, 1110 cm⁻¹. Melting point: 154-156° C.

N,N′-di(trifluoromethylbenzene)-2,3-diiminoethane

Under nitrogen, 3.24 g (10 mmol) of 2,4-dibromoterephthalic acid wascombined with 10 g of H₂O; 1.10 g (10.4 mmol) of Na₂CO₃ was then added.The mixture was heated to reflux with stirring for 30 min, remainingunder a nitrogen atmosphere. Another 1.54 g (14.5 mmol) of Na₂CO₃ wasadded to the reaction mixture and reflux was continued for 30 minutes.Separately, 22 mg (0.01 mol equiv) of CuBr₂ and 69 mg (0.02 mol equiv)of N,N′-di(trifluoromethylbenzene)-2,3-diiminoethane were combined undernitrogen, followed by addition of 2 mL H₂O under air. This solution wasadded to the stirred reaction mixture via syringe at with 80° C. undernitrogen and stirred for 26 h at 80° C. After cooling to 25° C., thereaction mixture was acidified with HCl (conc.), producing a dark yellowprecipitate. The precipitate was filtered and washed with water anddried. The conversion and selectivity of 2,4-hydroxyterephthalic acidwere determined to be 100% and 72%, respectively, by ¹H NMR. The netyield was determined to be 72%.

Where an embodiment of this invention is stated or described ascomprising, including, containing, having, being composed of or beingconstituted by certain features, it is to be understood, unless thestatement or description explicitly provides to the contrary, that oneor more features in addition to those explicitly stated or described maybe present in the embodiment. An alternative embodiment of thisinvention, however, may be stated or described as consisting essentiallyof certain features, in which embodiment features that would materiallyalter the principle of operation or the distinguishing characteristicsof the embodiment are not present therein. A further alternativeembodiment of this invention may be stated or described as consisting ofcertain features, in which embodiment, or in insubstantial variationsthereof, only the features specifically stated or described are present.

Where the indefinite article “a” or “an” is used with respect to astatement or description of the presence of a step in a process of thisinvention, it is to be understood, unless the statement or descriptionexplicitly provides to the contrary, that the use of such indefinitearticle does not limit the presence of the step in the process to one innumber.

Where a range of numerical values is recited herein, unless otherwisestated, the range is intended to include the endpoints thereof, and allintegers and fractions within the range. It is not intended that thescope of the invention be limited to the specific values recited whendefining a range.

1-15. (canceled)
 16. A process for preparing 2,5-dialkoxyterephthalicacid comprising the steps of: (a) contacting a 2.5-dihaloterephthalicacid, as described generally by Formula III

wherein X:=Cl, Br, or I, with base in water to form therefrom thecorresponding dibasic salt of the 2,5-dihaloterephthalic acid; (b)contacting the dibasic salt of the 2,5-dihaloterephthalic acid with basein water, and with a copper source in the presence of a ligand thatcoordinates to copper, to form the dibasic salt of2-5-dihydroxyterephthalic acid from the dibasic salt of 2,5-dihaloterephthalic acid at a solution pH of at least about 8; whereinthe ligand comprises a Schiff base; (c) optionally, separating thedibasic salt of 2,5-dihydroxyterephthalic acid from the reaction mixturein which it is formed; (d) contacting the dibasic salt of2,5-dihydroxyterephthalic acid with acid to form therefrom2,5-dihydroxyterephthalic acid; and (e) converting the2,5-dihydroxyterephthalic acid to a 2,5-dialkoxyterephthalic acid.
 17. Aprocess according to claim 16 wherein the 2,5-dihydroxyterephthalic acidis contacted under basic conditions with a dialkyl sulfate of theformula R⁹ R¹⁰ SO₄ wherein R⁹ and R¹⁰ are each independently asubstituted or unsubstituted C₁₋₁₀ alkyl group.
 18. A process forpreparing a compound, monomer, oligomer or polymer from2,5-dihydroxyterephthalic acid comprising the steps of: (a) contacting a2,5-dihaloterephthalic acid, as described generally by formula III

wherein X=Cl, Br, or I, with base in water to form therefrom thecorresponding dibasic salt of the 2,5-dihaloterephthalic acid; (b)contacting the dibasic salt of the 2,5-dihaloterephthalic acid with basein water and with a copper source in the presence of a ligand thatcoordinates to copper, to form the dibasic salt of2,5-dihydroxyterephthalic acid from the dibasic salt of2,5-dihaloterephthalic acid at a solution pH of at least about 8;wherein the ligand comprises a Schiff base; (c) optionally, separatingthe dibasic salt of 2,5-dihydroxyterephthalic acid from the reactionmixture in which it is formed; (d) contacting the dibasic salt of2,5-dihydroxyterephthalic acid with acid to form therefrom2,5-dihydroxyterephthalic acid; and (e) subjecting the2,5-dihydroxyterephthalic acid to a reaction to prepare therefrom acompound, monomer, oligomer or polymer.
 19. A process according to claim18 wherein a polymer prepared comprises apyridobisimidazole-2,6-diyl(2,5-dihydroxy-p-phenylene) polymer.
 20. Aprocess according to claim 16 further comprising a step of subjectingthe 2,5-dialkoxyterephthalic acid to a reaction to prepare therefrom acompound, monomer, oligomer or polymer.